1. Field of the Invention
The present invention relates to a method of manufacturing a surface-coated cutting tool with excellent abrasion resistance, and particularly, to a method of manufacturing a surface-coated cutting tool with excellent abrasion resistance in which an aluminum oxide layer is formed by a sol-gel method on the surface of a tool body made of tungsten carbide-based cemented carbide, titanium carbonitride-based cermet, high-speed steel, or a cubic boron nitride-based ultra-high-pressure sintered body (hereinafter, simply referred to as the cutting tool body), or the outer-most surface of a hard-coating film coated on the surface of the cutting tool body.
2. Description of Related Art
Hitherto, it has been known that a hard-coating film made of a carbide, nitride, carbonitride or the like of at least one element selected from the groups IVa, Va and VIa in the periodic table is formed to improve the abrasion resistance of a cutting tool.
Among the hard-coating films, an α-type aluminum oxide layer is formed as the outer-most surface layer of the hard-coating film made of a carbide, nitride, carbonitride or the like of at least one element selected from the groups IVa, Va and VIa in the periodic table in many cases from the viewpoint of excellent thermal stability, low reactivity, and high hardness.
Normally, chemical vapor deposition (CVD) is employed as a method of forming the aluminum oxide layer. However, forming the aluminum oxide layer by physical vapor deposition (PVD) or a sol-gel method is also known.
For example, as shown in Japanese Unexamined Patent Application, First Publication No. 2004-124246, a method of forming an α-type alumina layer under a low-temperature condition (1000° C. or lower) to prevent transformation and deterioration in characteristics of a cutting tool body and a hard-coating film is proposed. In the method, a hard-coating film made of a nitride, carbide, carbonitride, boride, oxynitride or oxycabonitride including, as essential components, Al and at least one element selected from the group consisting of the groups IVa, Va and VIa and Si is formed by physical vapor deposition (PVD) on the surface of a cutting tool body. Then the hard-coating film is oxidized to form an oxide-containing layer. As a result, an alumina layer essentially having an α-type crystal structure and excellent in abrasion resistance and heat resistance as an outer-most layer is deposited on the oxide-containing layer by physical vapor deposition (PVD).
In addition, as shown in Japanese Unexamined Patent Application, First Publication No. 2007-75990, a surface-coated cutting tool having a hard-coating layer deposited thereon by physical vapor deposition (PVD) is proposed. In the surface-coated cutting tool, the first layer is constituted by a (Ti,Al)N layer and the second layer is constituted by an aluminum oxide layer (preferably, γ-type alumina layer).
Furthermore, as shown in Japanese Unexamined Patent Application, First Publication No. 2006-205558, a method of manufacturing an aluminum oxide-coated structure with excellent mechanical characteristics and durability is proposed. In the method, a base material is coated with the first alumina layer formed of alumina having an amorphous crystal structure, alumina having a γ-type structure, or a mixture thereof by a sol-gel method, and the second alumina layer essentially having γ-type is formed by sputtering.
By using the above-described conventional surface-coated cutting tools (hereinafter, simply referred to as the coated tools), which are coated with the hard-coating film and an aluminum oxide layer formed on the outer-most surface of the hard-coating film, abrasion resistance on the rake face of the coated cutting tool is improved in the steel cutting or the like. The reason for the improvement is that α-type alumina has high heat stability and non-reactiveness.
Japanese Unexamined Patent Application, First Publication No. 2004-124246 proposes the formation of an α-type alumina layer under low-temperature conditions by physical vapor deposition (PVD). In the deposition of the aluminum oxide layer, the hard-coating layer needs to be oxidized first to form the oxide-containing layer on the surface of the oxidized hard-coating layer. However, in the aluminum oxide layer by the PVD method, adhesion between the oxide-containing layer and the aluminum oxide layer is not sufficient. In addition, as the aluminum oxide, the γ-type alumina is also present in addition to the α-type alumina. Because of these problems, sufficient heat resistance is not obtained. As a result, the cutting tool with an α-type alumina layer deposited by PVD cannot show sufficient cutting performance for a long time period of use.
In addition, in Japanese Unexamined Patent Application, First Publication No, 2007-75990 and Japanese Unexamined Patent Application, First Publication No. 2006-205558, since the formed aluminum oxide is γ-alumina, stability at high temperature is poor, and during high-speed cutting, satisfactory cutting performance cannot be exhibited.